1. Field of the Invention
The present invention relates generally to a fuel cell, and more particularly to a fuel cell having a pump or other gas transfer apparatus for moving gases in the fuel cell, as well as to a method for construction of and operation of a fuel cell.
2. Description of the Related Art
In a fuel cell, the chemical energy that is present in hydrogen and the oxidant (oxygen) is cleanly, quietly and efficiently converted electrochemically into electrical energy. The hydrogen is oxidized at the anode (negative pole) and the oxygen (or oxygen from the air) is reduced at the cathode (positive pole) of a single cell. The catalyst on the anode promotes the oxidation of hydrogen molecules into hydrogen ions (H+) and electrons: the hydrogen ions migrate through a special membrane to the cathode, where the cathode catalyst causes the combination of the hydrogen ions, electrons and oxygen to produce water. In this construction, the membrane is a polymer membrane so that the fuel cell is a so-called Proton Exchange Membrane Fuel cell (or PEMFC or PEM). The membrane conducts the hydrogen ions from one side to the other while blocking the free electrons but does so more efficiently when fully hydrated.
When connected to an electrical circuit, the electrical energy of the fuel cell produces a flow of electrons through the external circuit as electric current, which can be used, for example, to run a direct current (DC) electric motor. For utilization in an AC circuit, an inverter provides alternating current (AC) for those kinds of applications.
The electrodes may be formed by a thin layer of a catalyst applied to an appropriate backing placed on the opposite surface of the thin polymer membrane. Two bipolar plates are positioned against this backing, one on each side of the membrane. The bipolar plates have two functions: transmission of electrons through the elementary cells and release of heat to the external environment. The side of the bipolar plates facing the membrane electrode assembly (MEA) may be provided with ribs, which allow for the distribution of the gases (hydrogen and air) and the discharge of the resultant product water.
Increased power is achieved in fuel cell technology by enlarging the cell area (to handle an increase in the amperage requirements) and by combining a number of single cells in series to produce a fuel cell stack. The bipolar plates are configured to handle increased voltage requirements.
The several types of fuel cells are characterized by means of the electrolyte type. The electrolyte in between the electrodes defines the operating temperature of the fuel cell and a suitable catalyst can be selected for that operating temperature.
There is a major need for standby power for munitions production suitable for military applications. Munitions today are “smart” which means they have embedded electronics to aid in achieving hits on the desired targets. This use of electronics requires electricity to power the embedded hardware and software.
Currently, batteries and in particular lithium batteries are employed in most smart munitions. However, since munitions are generally produced during periods of non-use and are for later use during periods of conflict, storage or “shelf life” becomes a critical issue in this application. Batteries that are embedded in such devices must be capable of long term survival, requiring continued reliably for perhaps decades in storage, and generally under the most demanding environmental conditions. As an alternative, the batteries may need to be put into the munitions immediately prior to use of the munitions, not something one would want to do in combat. These batteries are called “reserve” batteries in the military.
Thermal reserve batteries are employed in some munitions but more commonly are used in bombs and missiles. The only difference in operating function between lithium batteries and thermal batteries is that thermal batteries are generally used for higher power applications. Beyond that, thermal reserve batteries are generally subject to the same demanding operating conditions as the lithium batteries.
U.S. Published Patent Application No. 2003 0152815 discloses microscopic batteries that are integrated or integratable with and provide internal power to MEMS (microelectromechanical systems) and integrated microcircuits, either on a retrofit or original manufacture basis. The MEMS involve the fabrication and use of miniature devices, which comprise microscopic moving parts (such as motors, relays, pumps, sensors, accelerometers, etc.). The MEMS devices can be combined with integrated circuits, and can perform numerous functions. For example, military applications for remote sensors and accelerometers include: safing and arming of fuses; friend or foe identification; embedded sensors for system integrity monitoring; communications systems monitoring, such as with satellites; low power mobile displays; flexible sensing surfaces; and numerous others. The microscopic batteries of patent publication application No. 2003 0152815 do not employ fuel cell technology due to the perceived limitation of providing sufficient power to drive the microdevices.
U.S. Pat. No. 6,506,513 and U.S. Published Patent Application No. 2003 0082421 each disclose a fuel cell assembly in which a fuel tank is located separate from the fuel cell and feeds the fuel to the cell via capillary action using a fuel permeating material U.S. Published Patent Application No. 2003 0129464 discloses a fuel cell assembly employing a separate fuel source which is rupturable by a needle for drawing out the fuel which is supplied to the fuel cell.
Although generators could be considered as standby power sources, their large size precludes them from all but the most energy intensive applications, so they are not normally considered where small size is necessary, but may be utilized when size is not a concern. Batteries in all their many types and sizes fill most short and medium shelf life niches with little problems. It's only where the shelf life requirements go into the decades that traditional batteries start to have failure issues because of their inherent chemical nature.